TA

Total alkalinity (TA) is the measure of your pool waters ability to resist pH changes. Technically, TA is defined as the sum of all of the concentrations chemical ion species in your pool water that can react with (or consume) a hydrogen ion (H+). The vast majority of your water’s alkalinity comes from the dissolved inorganic carbon (DIC) in it. DIC is primarily in the form of carbonates - dissolved or aqueous CO2, bicarbonate ion (HCO3-) and carbonate ion (CO32-). However, cyanurates from your stabilizer (cyanuric acid) as well as borates contribute to your water’s alkalinity.

The easiest analogy for TA is this - the water’s TA is a lot like a shock-absorber on a car. It keeps the car from bouncing around wildly when you drive. If your water has very low TA, then the pH of the water can bounce around wildly like a person being attached to a bungee cord. If the water has too much alkalinity, then the pH will change very slowly and, in the case of excess carbonate alkalinity (which all pool water has), there will be upward pressure on the pH to constantly rise (the chemical reactions that govern this are explained in more detail in the forum threads).

TA and pH go hand-in-hand. When TA gets too low (near zero), your pool water’s pH can crash down to values lower than 4.5. When TA is too high, the outgassing of dissolved carbon dioxide and subsequent chemical reactions involving the bicarbonate alkalinity will cause hydrogen ions to be consumed and your pH will rise. Just like pH, there is not “optimal” TA value - your optimal TA value is the value at which your pH is most stable (longest times between acid additions). Typically, people find that a TA somewhere between 80-100ppm works well enough.

However, if a pool is experiencing constant acid demand and pH rises too quickly, TA can be safely lowered as far as 50ppm or so to try to compensate for this. Despite what the “pool experts” will say, keeping your TA on the low end will not “rot out your equipment” or “destroy your plaster surfaces”.

Like pH, TA is a quantity used to calculate something called the calcite saturation index (a variant of the Langlier Saturation Index) and, as long as your CSI is within the “balanced” limits, then it does not typically matter what the individual pH or TA values are. More about CSI later.

The simplest way to raise TA is with baking soda (sodium bicarbonate or sodium hydrogen carbonate). In fact, if you look at the ingredient in the chemical bottle that pool stores sell as “alkalinity increaser”, it is precisely that, baking soda!! And, it is often 2X to 3X the price of the stuff in your grocery store.

It is often best to make large TA adjustments in a couple of steps, testing the water after each one, as adding large quantities of baking soda can raise the PH a little and you don't want the PH going out of range.

TA is lowered every time you add acid to your water (again, a complicated series of chemical reactions that won’t be described here).

If you need to lower your TA level aggressively, see How To Lower Total Alkalinity.